(CNN) -- President Bush has opened a slight lead over Sen. John Kerry in the pivotal battleground state of Florida, but the race still remains within the margin of error 40 days before the election, according to a CNN/USA Today/Gallup poll released Thursday.

The poll also found that Republicans in the Sunshine State were more enthusiastic about voting this year than Democrats, but voters overall were less optimistic about economic conditions than they were in July, before three hurricanes battered the state. And forecasters predict another may be on the way.

Thursday's poll in Florida was the fourth CNN/USA Today/Gallup battleground state poll released this week. Bush also led in the other three states surveyed -- Iowa, Nevada and West Virginia.

Also Thursday, two other polls showed Bush opening up a significant lead in another swing state, Wisconsin, which went Democratic four years ago.

Among likely voters surveyed in Florida, 49 percent said they supported Bush, 46 said they supported Kerry and 2 percent expressed support for independent Ralph Nader. Among registered voters, 47 percent chose Bush, 45 percent chose Kerry and Nader's support remained at 2 percent.

The margin of error was plus or minus 4 percentage points.

Nader will be on the ballot in Florida, after the state's Supreme Court last week turned down a challenge to his candidacy brought by Democrats.

Another Florida poll that came out Thursday, conducted by Quinnipiac University, showed a larger lead for the president among registered voters, with Bush at 49 percent, Kerry at 41 percent and Nader at 5 percent, with a margin of error of plus or minus 3.5 percentage points.

Asked their feelings about the Florida economy, 41 percent of the respondents in the CNN/USA Today/Gallup poll rated it excellent or good, down from 51 percent in July. In the latest poll, 57 percent said the economy was only fair or poor, compared with just 47 percent who thought that in July.

Asked if they were more enthusiastic than usual about voting this year, 63 percent of Republicans said "yes," compared with just 56 percent of Democrats. Forty-two percent of Democrats said they were not more enthusiastic than usual, compared with 37 percent of Republicans who felt that way.

That puts the gap between more enthusiastic and less enthusiastic Republicans at 26 percent, compared with 14 percent for Democrats.

In this week's earlier polls, Bush had 50 percent support among likely voters surveyed in Iowa, with Kerry at 44 percent and Nader at 2 percent. Among registered voters, Bush had 48 percent; Kerry, 43 percent; and Nader, 3 percent. The margin of error was plus or minus 4 percentage points.

Bush's lead in Iowa, which Democrat Al Gore carried in 2000, marked an unwelcome shift for Kerry. The Hawkeye State was where the Massachusetts senator revived his foundering campaign during January's Democratic precinct caucuses, and he had consistently led Bush in the polls until the president's bounce after the Republican National Convention.

In West Virginia, Bush had 51 percent support among likely voters, with Kerry at 45 percent and Nader getting less than one-half of 1 percent. Among registered voters, the president's support remained at 51 percent, Kerry dropped to 42 percent and Nader came in with 2 percent. The margin of error was plus or minus 4 percentage points.

Bush carried West Virginia in 2000, but the Kerry camp has made the state -- a union stronghold with twice as many registered Democrats as Republicans -- a prime target. The CNN/USA Today/Gallup poll showed that the outnumbered Republicans were more enthusiastic than Democrats in the Mountain State about voting this year.

In Nevada, Bush was the choice of 52 percent of likely voters surveyed, with Kerry at 43 percent and Nader at 1 percent. The race was much closer among registered voters, with Bush at 48 percent; Kerry, 46 percent; and Nader, 2 percent. The margin of error was plus or minus 4.5 percentage points.

The president also carried Nevada four years ago, but his narrow margin of victory and the state's large Latino population have encouraged the Kerry campaign to target the state. This week's poll showed Democrats more enthusiastic than Republicans about voting in the Silver State, but the margin was slight.

In Wisconsin, the Badger Poll conducted by the University of Wisconsin Survey Center found that among registered voters surveyed, Bush had 52 percent support, compared to just 38 percent for Kerry and 4 percent for Nader. The margin of error was plus or minus 4.5 percentage points.

An ABC News poll in Wisconsin put Bush at 53 percent among likely voters surveyed, with Kerry at 43 percent and Nader at 1 percent, with a margin of error of plus or minus 4 percentage points. Among registered voters surveyed, the poll found 50 percent for Bush, 44 percent for Kerry and 2 percent for Nader, with a margin of error of plus or minus 3 percentage points.